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CWE-409Weakness · CWE-409

CVE-2026-15709

HIGH · 7.5 CVSS v3.1 Published 2026-07-14
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
84/100
Remediation priority · High
Remotely reachable No privileges Zero-click 6 weeks old

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
A flaw was found in libsoup's WebSocket implementation when using the permessage-deflate extension. The extension's decompression loop (inflate()) processes data in chunks without enforcing an upper boundary limit on the output buffer size. While libsoup limits the incoming compressed frame size via max_incoming_payload_size, it fails to track or limit memory allocation during decompression. A separate check for decompressed size (max_total_message_size) exists but executes only after inflation is complete, and it is entirely disabled by default for client connections. A remote, unauthenticated attacker can exploit this by sending a small, highly compressed payload (a decompression bomb), causing unbounded memory allocation that triggers an Out-of-Memory (OOM) crash and a Denial of Service (DoS).

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

A memory exhaustion vulnerability exists in libsoup's WebSocket permessage-deflate decompression implementation. The inflate() loop allocates memory for decompressed output without enforcing an upper bound, allowing an attacker to send a small compressed payload (decompression bomb) that expands to huge memory allocations, causing OOM crashes. The protective max_total_message_size check exists but is disabled by default for client connections.

MitigationEnable and enforce max_total_message_size limits in libsoup's WebSocket configuration, and add explicit output buffer size limits during the inflate() decompression loop to bound memory allocation regardless of compression ratio.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify libsoup installation and version
    Run 'pkg-config --modversion libsoup-3.0' or 'pkg-config --modversion libsoup-2.4' depending on the version in use, or check your system's package manager for libsoup version
    Affected if The installed version falls within any affected version range for this vulnerability
  2. Verify WebSocket with permessage-deflate is enabled
    Inspect your application code or configuration for WebSocket connection setup using libsoup; look for SoupWebsocketConnection usage with permessage-deflate extension negotiated (check for 'permessage-deflate' in WebSocket subprotocol or headers)
    Affected if Your application uses libsoup WebSocket connections with permessage-deflate compression enabled (this is required for the vulnerable code path)
  3. Check max_total_message_size configuration for client connections
    Review libsoup WebSocket configuration or your application code; look for soup_websocket_client_set_massage_limits() or similar API calls; for client connections specifically, verify whether max_total_message_size is explicitly set (it is disabled by default for client connections)
    Affected if max_total_message_size is NOT explicitly set for client WebSocket connections, meaning the protective limit is not enforced (this is the default vulnerable state)
  4. Confirm application role uses client-side WebSocket connections
    Determine if your application initiates WebSocket client connections (using soup_websocket_client_connect() or similar) rather than only accepting server connections
    Affected if Your application creates client WebSocket connections; the vulnerability specifically notes that max_total_message_size is disabled by default for client connections

You are affected if your environment uses libsoup with WebSocket permessage-deflate compression AND uses client WebSocket connections without explicitly setting max_total_message_size limits, allowing unbounded memory allocation during decompression.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

From vendor data
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Enable and enforce max_total_message_size limits in libsoup's WebSocket configuration, and add explicit output buffer size limits during the inflate() decompression loop to bound memory allocation regardless of compression ratio.

Have this fixed Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing6.0 h
  • Review / QA4.0 h
22.0 hours of engineering $3,860
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-15709 in production — separate from our analysis above.

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What this is

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What belongs here
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  • Version or environment caveats, and links to real fixes
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